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Repeat Photography

Repeat Photography for Nature Conservation

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Comparisons of repeated photographs show changes of interest for nature conservation. Photographs show changes in vegetation (Turner et al 2003), glaciers (Tarr and Martin 1914), sand dunes (Haynes 1980), details of plant growth (Crimmins and Crimmins 2008), and small changes in land surface features (Trimble and Lund 1982). Photographs are easy to repeat, making them one of the most economical means to observe change.

The white rock in the photo at right appeared sometime during a four-day interval between photographs.

For example, a recent discovery made with repeated photographs shows that a rock appeared near the NASA Mars Land Rover Opportunity. The photo match isn’t very good, but there are enough recognizable points to see that the photos show the same scene.

Repeating photographs yields large rewards for minimal effort. You can repeat any photograph simply by holding your camera in the same place and pointing it in the same direction as the original. Of course, finding the same place can be difficult. Turner (2007) provides one of the best descriptions of how to rediscover the site of a previous photograph. The process is simple trial and error. With the original photo in hand, you move about until the scene matches the photo. Turner refines the process with suggestions that are helpful in cases where the location of the original camera station is difficult to find.

If you think you might repeat a photograph, you can record camera position so that future photos will be easier to line up. Pairs of photographs are easier to compare if you take them on the same dates and at the same time of day, so you want to record those details too.

You can repeat photographs with any combination of camera and lens. If you use a lens with a smaller field of view than the original lens, information on the margins of the scene will be lost, but if you aimed the camera at the center of the original scene the geometric properties of the images will match (Malde 1973). For analysis and presentation, you can crop photographs to show the same scene.

Here are some examples of repeat photography. The first pair shows that a glacier completely melted, the second pair shows vegetation changes, and the third pair shows a scene with almost no change.

Boulder Glacier, Glacier Park (USGS Photo Library)

The Boulder Glacier photos show the glacier disappeared during the 56-year interval between photographs. The photos below show that a landscape dominated by sagebrush in 1869 became weed-dominated during the 140 year interval between photographs. Sagebrush covered the slope beyond the train in 1869. No sagebrush is visible there today. I also repeated this photo in 1978. At that time, about half the sagebrush was gone.

Russell 1869

Big Trestle photographed by AJ Russell in 1869 and repeated by Garry Rogers in 2009.

The photos below were taken on an almost inaccessible ridge that has never been grazed by livestock. From the 1916 photo by Homer Shantz, to the 1976 photo by me, there was almost no change. Look closely at the foreground. You can see small rocks, plants, and a fallen tree branch in their original positions.

Almost no change from the 1916 H. Shantz photo at left to the 1976 G. Rogers photo at right.

Become a Repeat Photographer

You can easily get and repeat historical photographs of your area. Museums, libraries, and government agencies have photo collections. In the United States, the U. S. Geological Survey provides an online collection of 30,000 historical photographs that you can download at no charge. The U. S. Geological Survey Repeat Photography Archive at the University of Arizona (Webb et al. 2007) has more than 12,000 pairs of repeated photographs. You can send your location (latitude and longitude) to the Archive and request a search to see what is available.